1. Field of the Invention
The present invention relates generally to differential pressure flow sensors for use in pressure flow lines and that provide a signal when a flow rate exceeds a predetermined rate and in particular relates to a differential pressure flow sensor utilizing first and second thin metallic sections, the first section having one of several planar shapes and the second section being formed of two parallel conductor arms, the two sections being detachably connected to each other to form a flow sensor switch having a normally closed electrically conductive switch path, the flow sensor being mounted in a common plane between first and second annular insulative support members or rings across a central opening defining a flow passageway such that a predetermined flow in the pressure flow line detaches the first and second metallic sections from each other to open the normally closed switch and provide an indication of an open conductive path.
2. Description of Related Art
A commonly assigned copending application filed of even date herewith, incorporated by reference herein in its entirety, and entitled "Differential Pressure Flow Sensor Using Multiple Layers of Flexible Membranes" describes a differential pressure flow sensor for use in very low pressure flow lines that includes at least first and second layers of flexible plastic membranes mounted on a support member and extending across the central flow passageway of the very low pressure line. The at least first and second layers of the flexible plastic membranes are in loose-fitting superimposed relationship with respect to each other to provide a membrane discontinuity and allow a predetermined bleed flow rate therethrough. An electrically conductive strip of flexible material is placed in juxtaposed relationship with the at least first and second layers of flexible plastic membrane. First and second electrical contacts are formed as part of the conductive strip for providing an indication of a closed or open conductive switch path through the conductive strip. In order to accomplish this indication, the conductive strip has a normally closed switch portion completing an electrical circuit between the first and second contacts, the switch being opened when the flow rate in the line exceeds the bleed flow rate through the at least first and second membranes with the very low flow pressure against the membranes opening the switch contacts to provide an indication of an open conductive path. Such a sensor is commonly known as a "slip-joint" type of sensor. The sensor as disclosed in the commonly assigned copending application, as stated, opens by the flow pressure forcing the membranes against one portion of the "slip-joint" conductive strip thus separating the electrical contacts and opening the circuit.
Another prior art type "slip-joint" type of sensor has a first outer annular support ring, an annular metallic conductive ring, an insulated center annular support ring, a second annular metallic conductive ring, and a fifth outer insulated support ring. The switch portion is formed of first and second elongated metallic sections one of which has an outer end connected to the first one of the metallic annular rings and a second portion having an outer end connected to the second spaced metallic annular ring. The second portion has a U-shaped inner end that slidably receives a flat inner end of the first section thus forming switch contacts. The conductors are connected to the first and second annular metallic rings to provide an indication of an open switch.
Such a sensor is important because it has a relatively large flow-through area with only the metallic switch in the flow path to detect the pressure flow. However, they require relatively high flow rates and high pressure differentials to operate. In addition, one end of the elongated metallic switch is electrically attached to one of the annular metallic rings in one plane and the other end is electrically attached to the other of the annular metallic rings in a second plane separated from the first annular metallic ring by an insulating member. Thus, these sensors are expensive because they require full diameter annular sheet metal rings spaced from each other by an insulated annular ring and to which the ends of the switch portion are connected.
It would be advantageous to have a "slip-joint" type of sensor without either membranes being required or without requiring the electrical contacts to electrically connect a first metallic annular ring in a first plane and a second metallic annular ring in a spaced second plane.